In prosematic (nonverbal) communication, terrestrial vertebrates engage in four main forms of behavior known in ethological terms as displays. In the past, there existed almost no information about brain mechanisms involved in the performance of such displays. In a long-term, comparative neurobehavioral investigation dealing with this question, utilization has been made of the mirror display of gothic-type squirrel monkeys. This display incorporates features of the challenge, courtship and signature displays of this species that have distinctive autonomic and somatic features. Earlier work on this project has shown that the internal pallidal segment of the striatal complex and its projecting pathways are essential for the performance of the display and that ascending pathways within the central tegmental tract are also involved. This year's experiments dealing with some unresolved questions concerning structures involved in the autonomic and somatic components of the display bring to a conclusion the phase of the investigation on brainstem mechanisms of the display.